Apparatus for continuous casting of metal ingots

ABSTRACT

In continuous casting of metal ingots by delivering molten metal to an open-ended mold while withdrawing cast ingot continuously from the open mold end and while directing liquid coolant onto the ingot surface emerging from the mold, the extremity of the ingot is supported by a stool that initially closes the mold open end and moves progressively away from the mold as the ingot is cast. The stool is provided with one or more drainage passages which are closed while the stool is in its initial position but open as the stool moves away from the mold to release fluid that may accumulate between the ingot extremity and the stool. The passages are defined by sliding portions of the stool that initially are held in passage-closing position, but are released for movement to passage-opening position when the stool moves away from the mold.

' [72 I Inventor:

' United States Patent Sergerie I 1 APPARATUS FOR CONTINUOUS CASTING OFMETAL INGOTS Felix Antoine Sergei-1e, Arvida, Quebec, Canada [73]Assignee: Alcan Research and Development Limited, Montreal, Quebec,Canada 22 Filed: March22, 1971 21 Appl.No.: 126,550

[52] US. Cl. ..164/274, 164/283, 164/281 [51] Int. Cl. ..B22d 11/08 [58]Field of Search ..164/89, 126, 128, 348, 82, 164/274, 88, 273, 276, 282,87, 136, 363,

Monndt ..164/282 X Nov. 14, 1972 Primary Examiner-J. Spencer OverholserAssistant Examiner-John S. Brown Attorney-Christopher C. Dunham, P. E.l-lenninger, Lester W. Clark, Robert S. Dunham, Gerald W. Griffin,Thomas F. Moran, Howard J. Churchill, R. Bradlee Boal, Robert Scobey andHenry T. Burke [57] ABSTRACT In continuous casting of metal ingots bydelivering molten metal to an open-ended mold while withdrawing castingot continuously from the open mold end and while directing liquidcoolant onto the ingot surface emerging from the mold, the extremity ofthe ingot is supported by a stool that initially closes the mold openend and moves progressively away from the mold as the ingot is cast. Thestool is provided with one or more drainage passages which are closedwhile the stool is in its initial position but open as the stool movesaway from the mold to release fluid that may accumulate between theingot extremity and the stool. The passages are defined by slidingportions of the stool that initially are held in passage-closingposition, but are released for movement to passage-opening position whenthe stool moves away from the mold.

13 Claims, 3 Drawing Figures APPARATUS FOR CONTINUOUS CASTING OF METALINGOTS BACKGROUND OF THE INVENTION This invention relates to thecontinuous casting of metal ingots, and in a specific sense is directedto new and improved procedures and apparatus for so-called direct chillcasting of ingots. By way of illustration, the

invention will be particularly described with reference to the castingof aluminum ingots, it being understood that the term aluminum as hereinemployed embraces pure aluminum metal and alloys thereof.

In a typical example of present-day practice, the continuous directchill casting of an aluminum ingot is effected in a shallow open-endedaxially vertical mold which is initially closed at its lower end by adownwardly movable platform or stool. The ingot is surrounded by acooling jacket through which a coolant fluid such as water iscontinuously circulated to provide external chilling of the mold wall.Molten aluminum is introduced to the upper end of the chilled mold, andas this molten metal solidifies in a region adjacent the periphery ofthe mold, the stool is moved downwardly. With effectively continuousdownward movement of the stool and correspondingly continuous supply ofmolten aluminum to the mold, there is produced an ingot of desiredlength.

The ingot emerging from the lower end of the mold is externally solidbut is still molten in its central portion; in other words, the poolofmolten aluminum within the mold extends downwardly into the centralportion of the downwardly moving ingot for some distance below the moldas a sump of molten metal having a progressively decreasing crosssection as the ingot solidifies inwardly until its core portion becomescompletely solid. As an important feature of the direct chill castingprocess, continuously supplied coolant fluid such as water is broughtinto direct contact with the outer surface of the advancing ingot belowthe mold. This direct chilling of the ingot surface serves both tomaintain the peripheral portion of the ingot in solid state and topromote internal solidification of the ingot.

In the initial stages of the casting operation, the butt of the ingotresting against the stool tends to shrink away from the stool at bothends owing to contraction incident to solidification and cooling.Frequently, the upper face of the stool is dished or concave to aid inretaining the initial portion of the cast ingot during solidification.Thus, very commonly, as'the ingot begins its descent from the mold, agap or space forms, between the ingot and the stool, in which fluid cancollect. The liquid coolant (e.g., water), directed against the ingotsurface in streams or jets, tends to collect in this space or cavity.

Such accumulation of stagnant liquid between the butt of the ingot andthe stool especially at the initial stage of casting is highlyundesirable. Heat from the solidifying ingot evaporates the trappedwater, causing a build-up of steam pressure beneath the ingot, and asthis steam from time to time escapes, the ingot is subjected to shocksand vibrations in a vertical direction. Especially within the first fewinches of travel of an ingot butt below the mold, the vibrations orbumps imparted to the ingot by entrapped and escaping steam betweeningot and stool cause disturbance of the molten metal meniscus in themold, and produce in the cast ingot structural defects such as surfacecracks and so called cold shuts for as much as 12 inches to 18 inchesabove the butt. These defects are not readily removable; hence it isofien necessary to cut off as scrap an uneconomically long portion ofthe ingot or (if the ingot is rolled into slab transversely of its longaxis) it may be necessary to shear an unusually wide edge portion of theslab to remove slab defects resulting from the aforementioned structuralflaws in the ingot butt.

The defects described above are encountered particularly often in thecasting of large ingots, e. g., of aluminum-magnesium alloys, having arectangular cross section (that is, cast in rectangular molds) andadapted for rolling into sheet. However, like problems may beencountered in the casting of other types of ingots as well.

SUMMARY OF THE INVENTION An object of the present invention is toeliminate or minimize the incidence of vertical vibrations or bumpsresulting from entrapment of fluid betweeningot butt and stool in thecontinuous direct chill casting of metal (e.g., aluminum) ingots, andthereby to eliminate or minimize the creation of structural defects inthe ingot butt portion by such bumps or vibrations. Another object is toprovide procedures and apparatus for preventing accumulation of fluidbetween an ingot butt and stool, such as might cause the aforementionedbumps and vibrations.

To these and other ends the present invention broadly contemplatesimprovements in procedures and apparatus for continuously casting ametal ingot in a mold having a wall laterally defining a casting zonewith an open outlet end, i.e., in casting operations of the type whereinmolten metal is in effect continuously delivered by suitable means intothe casting zone of the mold, and wherein a stool, initially closing theoutlet end of the mold and supporting the extremity of the ingot beingcast, is moved away from the mold outlet end for effecting continuousadvance of the ingot from the mold during casting, and wherein coolantliquid is directed by suitable means onto the surface of the ingotemerging from the mold.

The improvement in accordance with the invention broadly comprises theprovision of one or more drain passages in the stool, for conductingfluid away from a locality defined between the stool and the ingot butt,and means for closing the drain passage or passages while the stool isin its initial mold-closing position, such means being openable forpennitting discharge of fluid through the passage or passages as thestool moves away from the mold outlet end so that coolant liquidentering the locality between the ingot butt and the stool is dischargedtherefrom through the passage or passages. In a procedural sense, then,the invention contemplates the step of opening a drain passage orpassages in the stool as the stool advances away from the mold outletend for discharging any fluid that may collect or become entrappedbetween the stool and the ingot butt.

As a particular feature of the invention, the stool may comprise aportion fixed in relation to a supporting movable platform, and one ormore additional portions slidably movable in relation to thefirst-mentioned portion to open passages for discharge of fluid betweenthe ingot butt and the stool. The sliding portion or portions are soarranged that when they are in a first position they close the drainpassages of the stool and cooperate with the fixed portion of the stoolto support the solidifying ingot butt and to close off the outlet end ofthe mold with which the stool is used. For example, the sliding portionsmay be formed to engage and be retained by structure disposed inadjacent and essentially stationary relation to the mold when the stoolis in mold-closing position. Advance of the stool away from the moldthen releases the sliding portions which move as by the force of gravityto positions in which the drain passages are open to release fluid frombetween the ingot and the stool.

As thus embodied, the invention incorporates means for opening one ormore drain passages in the stool in response to movement of the stoolaway from the mold. Thereby, water from the coolant streams impinging onthe ingot surface just below the mold and collecting in the space formedbetween the contracting ingot butt and the stool is drained away (asliquid and/or steam) so that steam pressure cannot accumulate betweenthe ingot and stool to cause bumping of the ingot.

Further features and advantages of the invention will be apparent fromthe detailed description hereinbelow set forth, together with theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a simplified sectionalelevational view of a continuous casting apparatus embodying the presentinvention in a particular form;

FIG. 2 is an enlarged sectional elevational view of the stool in thecasting apparatus of FIG. 1 at a stage in the casting operation afterthe stool has moved away from the mold; and

PK]. 3 is an end view of the stool, taken as along the line 3 3 of FIG.2.

DETAILED DESCRIPTION Referring to the drawing, there is shown in FIG. 1a form of apparatus for continuously casting aluminum ingots, includingan axially vertical mold (open at its lower end) to which moltenaluminum metal 11 is supplied for casting an ingot 12. The mold l0,fabricated of a metal suitably resistant to deterioration under theconditions for casting aluminum, has a vertical inner wall 14 whichdefines an axially vertical casting zone 14a of desired horizontal crosssection (e.g., circular, square, or rectangular), it being understoodthat this mold wall configuration determines the cross-sectional shapeof the produced ingot; merely by way of specific illustration, referencewill be made herein to a mold which is rectangular, i.e., in crosssection, for producing an ingot of corresponding rectangular crosssection.

Surrounding the outer surface of the mold wall 14 is a cooling jacket 15shown for simplicity as formed of further wall portions cooperating withthe wall 14 to define and enclose an annular chamber 15a completelylaterally surrounding the casting zone. This enclosed chamber issupplied by suitable means (not shown) with a cooling fluid such aswater for chilling the mold wall 14, and is preferably kept continuouslyfilled with a flowing or circulating body of fluid, designated 16.

At the start of the casting operation, the lower end of the casting zone14a is closed by a stool 18 which is carried on a platform 19 that is inturn supported on a hydraulic ram 20. As molten aluminum in the castingzone solidifies around the lower portion of the periphery of that zone,the stool 18 and platform 19 are drawn slowly vertically downward byoperation of the hydraulic ram 20. The solidifying base of the ingotbeing cast, resting on the stool, then begins to emerge from the lowerend of the casting zone.

The mold apparatus is arranged to direct a spray or stream of coolingfluid such as water onto the emerging solidified ingot surfaceimmediately below the casting zone. Thus, as shown, there may beprovided a slit 22 in the lower wall of the cooling jacket 15, extendingentirely around the mold periphery, and oriented to direct water fromthe chamber 15a of the cooling jacket onto the surface of the emergingingot. This spray of water, striking the ingot surface, acts to enhancethe cooling and consequent solidification of the ingot as it movesdownwardly away from the mold. In this arrangement, water iscontinuously supplied to the chamber and is continuously dischargedthrough the slit 22 onto the ingot surface so that there is a continuousflow of coolant fluid for removing heat from the solidifying metal.

Molten aluminum is supplied to the mold from a body or source shown ascontained in a launder 26 positioned at a level above the mold andcommunicating therewith through an axially vertical dip tube 28 thatextends downwardly from the launder into the casting zone 14a in coaxialrelation to that zone. The lower end of dip tube 28 opens at a level inthe casting zone somewhat beneath the level of the molten aluminum pooltherein. A filter, baffle or the like may be positioned at or adjacentthe lower end of dip tube 28 within the mold for filtering and/ordirecting the supply of molten aluminum as the molten metal enters themold. For example, in FIG. 1 there is shown a floattype baffle 30,buoyantly supported in the molten aluminum pool 11 in surroundingrelation to the outlet end of the dip tube for directing the major flowof metal laterally (toward the side walls of the mold) and forcontrolling the level of molten metal in the mold by effectively closingoff the lower end of the dip tube incident to rise of molten metal abovea desired maximum level in the mold.

The foregoing structures are broadly conventional and their operation,for continuously casting an aluminum ingot, will be familiar to thoseskilled in the art. The present invention, as embodied in theillustrated casting apparatus, is directed to improvements in thestructure of the stool 18 for preventing accumulation of fluid betweenthe stool and the butt end of the ingot resting thereon. As embodied inprocedures that may be performed with the apparatus of FIG. 1, theinvention resides in steps for effecting discharge of fluid that mayaccumulate between the ingot butt end and the stool, all as now to bedescribed.

In accordance with the invention, in its illustrated embodiment, thestool 18 is made in three parts: a central body 34 fixed on the platform19, and two side members 35 respectively extending along opposite sidesof the central body and laterally slidable in relation to the centralbody. The upper surfaces of these three stool portions togetherconstitute the support surtending completely around the periphery of thestool (i.e., when the members 35 are in positions abutting the .body 34,as hereinafter further described) so as to give the ingot-supportingsurface a dished or concave contour which aids in supporting thesolidifying butt of the ingot at the start of the casting operation.

Each of the members 35 is slidable in a generally horizontal directiontoward and away from abutting engagement with the central stool body 34.When the members 35 abut the body 34, as shown in FIG. 1, they cooperatewith that body to form a continuous, unapertured stool-supportingsurface; the stool rim then formed by rim portions 36 is dimensioned tofit closely within the lower end of the mold casting zone. However, whenthey are moved away from the central body, the spaces then openedbetween the members 35 and the central body (as shown in FIG. 2)constitute drain passages 38 for discharge of any fluid that may havecollected on the upper surface of the stool. To aid in such drainage,the upper surface 34a of the stool central body 34 may be pitched orcambered so as to cause flow of liquid from surface 34a into thepassages 38.

The two side members 35 are mounted on outwardly sloping side portionsof the fixed stool body 34, in such manner that a space or passage 39for fluid flow is defined between the downwardly facing surface of eachmember 35 and the upwardly facing surface of the sub jacent portion ofbody 34. As best seen in FIG. 3, each member 35 is slidably supported atits ends by outwardly sloping flanges 40 formed integrally with andprojecting upwardly from the subjacent portion of the stool body 34. Inaddition, each member 35 has one or more centrally disposed lugs 42which project downwardly from its lower surface into a guide channel 43formed in thesubjacent portion of the body 34. The flanges 40 supportthe members 35 in upwardly spaced relation to the underlying portion ofbody 34 so as to define the desired fluid passages 39, while permittingthe above-described outward sliding movement of the members 35 inrelation to body 34. The lugs 42 in cooperation with the channels 43prevent movement of the members 35 in directions transverse to thedesired direction of movement. In addition, stop means such as washers44 are mounted by screws 45 at the outer ends of the channels 43 forengaging the. lugs 42 to arrest, and thus limit outward movement of, themembers 35 at a position at which the members 35 are sufficiently spacedfrom body 34 to open the passages 38 as described.

Fixedly mounted on the outwardly facing side surface of each member 35is an outwardly projecting element 47 which is adapted to be engaged bya springloaded arm 48 when the stool is in position closing the lowerend of the mold and the members 35 are disposed in abutting relation tothe body 34. Two such arms 48 are mounted on respectively opposite sidesof the path of downward travel of the stool, in essentially stationaryrelation to the mold immediately below the lower end of the mold, forengagement with the elements 47 of the two members 35 respectively, toretain the members 35 in their initial passage-closing positions so longas the stool remains at the lower end of the mold. As the stool movesdownwardly away from the mold, however, the elements 47 of the members35 are carried downwardly out of engagement with their respectivelyassociated arms 48 (which may, as shown, bear rollers 49 at their endsengaging the elements 47), releasing the members 35 for outward slidingmovement to open the passages 38.-Except when restrained by the arms 48,the members 35 tend to move to their passage-opening positions under theforce of gravity (i.e., until arrested by stop washers 44) owing to theoutward and downward slope of the flanges 40 on which they rest. It willbe understood that the arms 48 are only illustrative of means forrestraining the members 35 in passage-closing position and releasing themembers for movement to passage-opening position in response to descentof the stool. Alternatively, for example, such retention (and release)of the members 35 may be effected by engagement of the rim portions 36of members 35 with the wall of the mold itself.

Thus in response to downward movement of the stool away from the mold,outward sliding movement of the members 35 opens the passages 38 so asto drain off any fluid collected on the upper surface of the stool. Thepassages 38, defined between the inner side surfaces of the members 35and the facing side surfaces of the central stool body 34, communicatewith the passages 39 defined between the lower surfaces of members 35and the subjacent surfaces of body 34 to provide a continuous path forflow of fluid from the upper surface of the stool to the exterior.

The operation of the described apparatus, and performance of the inethodof the invention therewith, may now be readily understood. With thestool in its initial position shown in FIG. 1 closing the lower end ofthe mold, and with the members 35 in their innermost positions as alsoshown in FIG. 1, molten metal is introduced to the mold, a suitable flowof coolant being circulated through and below the mold. The effect ofthe coolant is to solidify the peripheral portions of the molten metalin the mold. As solidification proceeds, the butt of the ingot beingformed contracts upwardly away from the stool surface on which it rests,so that a gap or space (shown at 50in FIG. 2) is defined between thecentral portion of the butt and the stool.

Until the stool begins to move downwardly, the sliding members 35, beingat their innermost positions, close the passages 38 so that liquidcannot flow downwardly therethrough. This initial closing of thepassages 38 serves to prevent leakage of molten aluminum through thosepassages at the start of the casting operation. However, such leakage isno longer a problem once the butt has solidified.

The descending motion of the stool is now initiated, and as theprojecting elements 47 of the sliding side members 35 move below thearms 48 (i.e., as, or shortly after, the stool rim 36 clears the lowerend of the mold and descends into a region in which coolant dischargedonto the side surface of the stool and of the descending ingot, tends toflow into the space 50 formed between the contracting ingot butt and thestool. If this liquid were permitted to accumulate, it would vaporizeowing to the heat of the solidifying ingot, and intermittently escapingsteam from this space 50 would tend to cause undesired verticalvibrations damaging to the structure of the butt portion of the ingotbeing formed. The opening of the passages 38 as the stool movesdownwardly away from the mold, however, drains the space 50; i.e., anyliquid and/or steam that may enter or tend to collect in the space 50flows downwardly and outwardly through the passages 38 and 39 definedbetween the members 35 and the stool central body 34, so that there canbe no significant build-up of pressure in the space 50 beneath theingot.

It has been found that the practice of the invention enables casting ofingots, e. g., aluminum ingots of large rectangular .cross section,which are substantially or entirely free of the types of butt defectsassociated with bumping or vertical vibrations such as result frombuild-up of fluid pressure between butt and stool. In conjunction withsuch practice of the invention, further reduction in intensity ofvertical vibrations may be attained by reducing the volume of coolant(e.g., water) impinging on the ingot surface below the mold; forexample, a pulsed discharge of water onto the ingot may be used toprovide such control of volume.

It is to be understood that the invention is not limited to the featuresand embodiments hereinabove specifically set forth but may be carriedout in other ways without departure from its spirit.

I claim:

1. Apparatus for continuously casting a metal ingot including a. a moldhaving a wall laterally defining a casting zone with an open outlet end;

b. means for delivering molten metal into said casting zone;

0. means including a stool for closing the outlet end of said mold, saidstool being positioned and adapted to support the extremity of an ingotbeing cast in said zone and being movable away from said mold outlet endfor effecting continuous advance of the ingot from the mold duringcasting; and

d. means for directing coolant liquid onto the surface of the ingotemerging from the outlet end of said mold;

wherein the improvement comprises e. said stool having at least onedrain passage for conducting fluid away from a locality defined betweensaid stool and said ingot extremity; and

f. means for initially closing said one drain passage and for openingsaid one passage to permit discharge of fluid therethrough after initialformation of the ingot extremity.

2. Apparatus as defined in claim 1, wherein said passage-closing meanscomprises means for opening said one passage in response to movement ofsaid stool away from said mold outlet end.

3. Apparatus as defined in claim 2, wherein said passage-closing meanscomprises a member carried by said stool and movable between apassage-closing position and a passage-opening position, said memberbeing retained in passage-closing position when said stool is inposition closing said mold outlet end, and being released, for movementto passage-opening position, upon movement of said stool away from saidmold.

4. Apparatus as defined in claim 3, wherein said passage-closing meansfurther comprises structure, positioned to engage said member when saidstool is in mold-closing position and adapted to remain essentiallystationary during movement of said stool away from said mold-closingposition, for retaining said member in passage-closing position whensaid stool is in moldclosing position, said member being released bydisengagement from said structure for movement to passageopeningposition upon movement of said stool away from said mold.

5. Apparatus as defined in claim 4, wherein said stool includes a firstingot-engaging portion movable in the direction of advance of the ingotfrom the mold, and wherein said member comprises a second ingot-engagingportion of said stool, laterally movable relative to said first portionbetween a first position in which said second portion abuts said firstportion, and a second position in which said second portion is spacedfrom said first portion to define between said first and second portionssaid one drain passage.

6. Apparatus for continuously casting a metal ingot including a. a moldhaving a wall laterally defining an axially vertical casting zone withan open lower end;

b. means for delivering molten metal into an upper region of saidcasting zone;

c. means including a stool for closing the lower end of said mold, saidstool being positioned and adapted to support the extremity of an ingotbeing cast in said zone and being movable downwardly away from said moldlower end for effecting continuous downward advance of the ingot fromthe mold during casting; and

. means for directing coolant liquid onto the surface of the ingotemerging from the lower end of said mold;

wherein the improvement comprises e. said stool having at least onedrain passage for conducting fluid away from a locality defined betweensaid stool and said ingot extremity; and

f. means for closing said one drain passage while said stool is inposition closing said mold lower end, said passage-closing means beingadapted to open as said stool moves downwardly away from said mold lowerend so that coolant liquid entering said locality between said ingotextremity and said stool is discharged therefrom through said onepassage.

7. Apparatus as defined in claim 6, wherein said passage-closing meanscomprises a member cooperating with said stool in supporting theextremity of said ingot, said member being supported by said stool andslidable in a direction transverse to the path of advance of said ingotbetween a position in which said member closes a drain passage and aposition in which said member opens said passage, said member beingretained in passage-closing position when said stool is in mold-closingposition and being released, for movement to passage-opening position,upon descent of said stool from said mold.

8. Apparatus as defined in claim 7, including a second passagetopeningmember identical to said firstmentioned member but disposed on anopposite side of the stool, both said members being disposed to engageportions of the extremity of said'ingot and to cooperate with said stoolin supporting said ingot extremity, and said members, when moved totheir passage-opening positions, cooperating with said stool to definedrain passages between said members and said stool on opposite sides ofsaid stool.

9. Apparatus as defined in claim 8, wherein said stool has a pitchedupper surface for promoting flow of fluid into said last-mentionedpassages.

10. Apparatus as defined in claim 8, wherein said stool and said membershave upwardly projecting rim portions cooperatively defining a dishedsurface in which said ingot extremity rests.

11. Apparatus as defined in claim 8, wherein said passage-closing meansfurther comprises structure, positioned to engage said members when saidstool is in mold-closing position and adapted to remain essentiallystationary during descent of said stool, for retaining said members inpassage-closing position when said stool is in mold-closing position,said members being released by disengagement from said structure formovement to passage-opening position upon descent of said stool fromsaid mold.

12. In continuous casting apparatus, in combination with an open-endedmold for receiving in molten form the material to be cast, a stool forclosing the outlet end of the mold, positioned and adapted to supportthe extremity of a body being cast in the mold and movable away from themold for effecting continuous advance of the body from the mold duringcasting, said stool having at least one drain passage for removing fluidfrom between the extremity of the body and the stool, said stool havinga surface facing the interior of said mold for contact with saidextremity of said body, and said passage opening through said surfaceinwardly of the periphery thereof.

13. Apparatus as defined in claim 12, including means supported by andcarried with said stool for initially closing said one passage prior tointroduction of molten material to said mold to prevent fiow of saidmolten material into the passage.

1. Apparatus for continuously casting a metal ingot including a. a moldhaving a wall laterally defining a casting zone with an open outlet end;b. means for delivering molten metal into said casting zone; c. meansincluding a stool for closing the outlet end of said mold, said stoolbeing positioned and adapted to support the extremity of an ingot beingcast in said zone and being movable away from said mold outlet end foreffecting continuous advance of the ingot from the mold during casting;and d. means for directing coolanT liquid onto the surface of the ingotemerging from the outlet end of said mold; wherein the improvementcomprises e. said stool having at least one drain passage for conductingfluid away from a locality defined between said stool and said ingotextremity; and f. means for initially closing said one drain passage andfor opening said one passage to permit discharge of fluid therethroughafter initial formation of the ingot extremity.
 2. Apparatus as definedin claim 1, wherein said passage-closing means comprises means foropening said one passage in response to movement of said stool away fromsaid mold outlet end.
 3. Apparatus as defined in claim 2, wherein saidpassage-closing means comprises a member carried by said stool andmovable between a passage-closing position and a passage-openingposition, said member being retained in passage-closing position whensaid stool is in position closing said mold outlet end, and beingreleased, for movement to passage-opening position, upon movement ofsaid stool away from said mold.
 4. Apparatus as defined in claim 3,wherein said passage-closing means further comprises structure,positioned to engage said member when said stool is in mold-closingposition and adapted to remain essentially stationary during movement ofsaid stool away from said mold-closing position, for retaining saidmember in passage-closing position when said stool is in mold-closingposition, said member being released by disengagement from saidstructure for movement to passage-opening position upon movement of saidstool away from said mold.
 5. Apparatus as defined in claim 4, whereinsaid stool includes a first ingot-engaging portion movable in thedirection of advance of the ingot from the mold, and wherein said membercomprises a second ingot-engaging portion of said stool, laterallymovable relative to said first portion between a first position in whichsaid second portion abuts said first portion, and a second position inwhich said second portion is spaced from said first portion to definebetween said first and second portions said one drain passage. 6.Apparatus for continuously casting a metal ingot including a. a moldhaving a wall laterally defining an axially vertical casting zone withan open lower end; b. means for delivering molten metal into an upperregion of said casting zone; c. means including a stool for closing thelower end of said mold, said stool being positioned and adapted tosupport the extremity of an ingot being cast in said zone and beingmovable downwardly away from said mold lower end for effectingcontinuous downward advance of the ingot from the mold during casting;and d. means for directing coolant liquid onto the surface of the ingotemerging from the lower end of said mold; wherein the improvementcomprises e. said stool having at least one drain passage for conductingfluid away from a locality defined between said stool and said ingotextremity; and f. means for closing said one drain passage while saidstool is in position closing said mold lower end, said passage-closingmeans being adapted to open as said stool moves downwardly away fromsaid mold lower end so that coolant liquid entering said localitybetween said ingot extremity and said stool is discharged therefromthrough said one passage.
 7. Apparatus as defined in claim 6, whereinsaid passage-closing means comprises a member cooperating with saidstool in supporting the extremity of said ingot, said member beingsupported by said stool and slidable in a direction transverse to thepath of advance of said ingot between a position in which said membercloses a drain passage and a position in which said member opens saidpassage, said member being retained in passage-closing position whensaid stool is in mold-closing position and being released, for movementto passage-opening position, upon descent of said stool from said mold.8. Apparatus as defined in claim 7, including a second pasSage-openingmember identical to said first-mentioned member but disposed on anopposite side of the stool, both said members being disposed to engageportions of the extremity of said ingot and to cooperate with said stoolin supporting said ingot extremity, and said members, when moved totheir passage-opening positions, cooperating with said stool to definedrain passages between said members and said stool on opposite sides ofsaid stool.
 9. Apparatus as defined in claim 8, wherein said stool has apitched upper surface for promoting flow of fluid into saidlast-mentioned passages.
 10. Apparatus as defined in claim 8, whereinsaid stool and said members have upwardly projecting rim portionscooperatively defining a dished surface in which said ingot extremityrests.
 11. Apparatus as defined in claim 8, wherein said passage-closingmeans further comprises structure, positioned to engage said memberswhen said stool is in mold-closing position and adapted to remainessentially stationary during descent of said stool, for retaining saidmembers in passage-closing position when said stool is in mold-closingposition, said members being released by disengagement from saidstructure for movement to passage-opening position upon descent of saidstool from said mold.
 12. In continuous casting apparatus, incombination with an open-ended mold for receiving in molten form thematerial to be cast, a stool for closing the outlet end of the mold,positioned and adapted to support the extremity of a body being cast inthe mold and movable away from the mold for effecting continuous advanceof the body from the mold during casting, said stool having at least onedrain passage for removing fluid from between the extremity of the bodyand the stool, said stool having a surface facing the interior of saidmold for contact with said extremity of said body, and said passageopening through said surface inwardly of the periphery thereof. 13.Apparatus as defined in claim 12, including means supported by andcarried with said stool for initially closing said one passage prior tointroduction of molten material to said mold to prevent flow of saidmolten material into the passage.